Methane oxidation in temperate soils: effects of inorganic N

Abstract

Additions of inorganic nitrogen (N) to an oak soil with significant potential for methane (CH 4) oxidation resulted in differential reduction in CH 4 oxidation capacity depending on N species added. Nitrate, rather than nitrite or ammonium, proved to be the strongest inhibitor of CH 4 oxidation in oak soil. Both high (CH 4 at 10 μl l −1) and low (CH 4 at 5 ml l −1) affinity CH 4 oxidation in oak soil was completely inhibited at a nitrate concentration similar to that present in an alder soil from the same experimental site. The alder soil showed no capacity for low affinity CH 4 oxidation. A ‘low nitrate’ forest soil (oak) showed high affinity, low capacity CH 4 oxidation upto around 1 ml l −1 CH 4, above which both high and low affinity CH 4 oxidation became apparent following a lag phase, indicating either an induced high affinity uptake mechanism or the existence of distinct low affinity and high affinity methanotroph populations. High affinity CH 4 oxidation became saturated at CH 4 concentrations >500 μl l −1, while low affinity CH 4 oxidation became saturated at ∼30 ml l −1 CH 4. In a ‘high nitrate’ forest soil (alder), CH 4 oxidation appeared to be due to high affinity CH 4 oxidation only and became undetectable at CH 4 concentrations >5 ml l −1.